Some existing glenoid components include a fixation peg or a fixation keel on the medial bone-facing surface. Some designs include multiple parallel pegs. The peg or keel may include surface features to enhance fixation, such as alternating ridges and grooves, flanges, and the like. The surface features frequently extend perpendicular to the axis of the peg or keel, because the primary direction of pull-out occurs along that axis. Glenoid components may experience failure by pull-out along the peg or keel axis, but other failure modes occur as well. The humerus, or humeral component, contacts the glenoid component in multiple locations on the glenoid lateral articular surface in vivo. Thus, forces which may cause loosening occur in multiple locations and along multiple vectors.
Glenoid components may experience forceful loading applied to the peripheral edge of the implant, which may cause the opposite side of the component to lift up. Forceful loading of the far posterior peripheral edge is a known common failure mechanism of glenoid components. This failure mode may be referred to as lever-out failure or rotational pull-out.
Glenoid components may also experience side-to-side translation in the superior-inferior direction or in the anterior-posterior direction. The most common direction is superior-inferior. Side-to-side translation is minimized when the implant peg, keel, or anchoring element is at least the same size as the bone tunnel into which it is inserted. However, the implant peg, keel, or anchoring element may be smaller than the bone tunnel, especially if the glenoid component will be fixed with bone cement. In this situation, the glenoid component is free to translate side-to-side, at least until the bone cement has hardened.
There is a need for an implant which resists axial pull-out, rotational pull-out (or lever-out), and translation.
The fundamental geometry of the anchoring elements disclosed herein provides inherent resistance to axial pull-out, rotational pull-out, and translation. The surface features disclosed herein are oriented in multiple planes to provide additional resistance to axial pull-out perpendicular to the back side of the glenoid component, pull-out along the axis of the dowel, and side-to-side translation in the superior-inferior or anterior-posterior directions.